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Mi Int2 Chemistry All 2010
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Transcript of Mi Int2 Chemistry All 2010
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Intermediate 2 Chemistry
General information for markers
The general comments given below should be considered during all marking. It should be noted thatthese are general marking principles and may be superseded by decisions made at the Markers Meeting.
1. Markers are reminded to read candidate responses in their entirety . If the candidate shows a clearunderstanding of the chemistry but does not use the exact words of the Marking Instructions theyshould still be given credit.
2. Markers are reminded that no comments are to be written on scripts. Comments such as ARITH,ERROR and BOD (Benefit of doubt) are not acceptable.
3. A guiding principle in marking is to give credit for (partially) correct chemistry rather than to lookfor reasons not to give marks.
Example 1: The structure of a hydrocarbon found in petrol is shown below.
CH 3
CH 3 CH 2 CH CH 2 CH 2 CH 3
Name the hydrocarbon.
Although not completely correct, the answer 3, methyl-hexane should gain the fullmark ie ignore wrong use of commas and dashes.
Example 2: A student measured the pH of four carboxylic acids to find out how their strength isrelated to the number of chlorine atoms in the molecule. The results are shown.
Structural formula pHCH 3COOH 1.65CH 2ClCOOH 1.27CHCl 2COOH 0.90
CCl 3COOH 0.51
How is the strength of the acids related to the number of chlorine atoms in themolecule?
Although not completely correct, an answer such as the more Cl 2, the stronger theid h ld g i th f ll k
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5. A right answer followed by a wrong answer should be treated as a cancelling error and no marksshould be given.
Example: What is the colour of universal indicator in acid solution?
The answer red, blue gains no marks.
6. If a right answer is followed by additional information which does not conflict, the additionalinformation should be ignored, whether correct or not.
7. Full marks should be awarded for the correct answer to a calculation on its own; the part marksshown in the Marking Instructions are for use when working is given.
8. A half mark should be deducted in a calculation for each arithmetic slip.
9. A half mark should be deducted for incorrect or missing units only when stated in the MarkingInstructions.
10. A half mark should be deducted for transcription errors.
11. Where a wrong numerical answer (already penalised) is carried forward to another step, no further penalty is incurred provided the end result is used correctly.
12. Ignore the omission of one H atom from a full structural formula provided the bond is shown.
13. A symbol or correct formula should be accepted in place of a name unless stated otherwise in theMarking Instructions .
14. If an answer comes directly from the text of the question, no marks should be given.
Example: Why do ionic compounds, like copper chloride, conduct electricity when in solution?
No marks for because they are ionic since the word ionic appears in the text.
15. Unless the question is clearly about a non-chemistry issue, eg costs in industrial chemistry, a non-chemical answer gains no marks.
Example:Why does the (catalytic) converter have a honeycomb structure?A response such as to make it work may be correct but it is not a chemical answerand the mark should not be given.
16. With structures involving an OH or an NH 2 group, a half mark should be deducted if theO or N are not bonded to a carbon ie OH CH 2 and NH 2 CH 2
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19. When it is very difficult to make a decision about a partially correct answer, a half mark can beawarded.
20. When marks have been totalled, a half mark should be rounded up.
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2010 Chemistry Intermediate 2
Marking Scheme
Section A
1 A 11 A 21 C
2 D 12 D 22 D
3 C 13 B 23 A
4 D 14 D 24 A
5 C 15 B 25 C
6 D 16 C 26 A
7 B 17 A 27 B
8 B 18 A 28 A
9 C 19 B 29 D
10 A 20 C 30 C
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Marking Instructions Chemistry Intermediate 2 2010
Section B
Question Acceptable Answer Mark Worth Worth 0
1 (a) Nucleus/nuclei 1 or 0 Protons and neutrons
(b) (i) 8Ignore any units given
1 or 0
(ii) Same/equal number of (positive) protons as (negative)electronsPositive charge of protons cancels negative charge ofelectronsProtons cancel out electrons
1 or 0 Same number of positive andnegative charges
Wrong charge eg negative protons cancel positiveelectrons
Nucleus attracts samenumber of protons andelectrons
Charges cancel( if no mention of
protons/electrons)
(iii) Alkali metals 1 or 0 Any named group 1 metalAlkaline metals
Alkali on its ownAlkaline on its ownReactive metalsGroup 1 metals
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Question Acceptable Answer Mark Worth Worth 0
2 (a) Endothermic 1 or 0 Chemical reactionFreezing
(b) (s) and (1) and (aq)Accept capitalsIgnore size
All 3 for 1 mark
1 or 0
(c) Solvent 1 or 0 SolutionAqueousSolute
(d)
8
2420726
=
or 8 on its own
1 or 0 Correct working shown but withwrong answer
An arithmetic mistake - mark
Correct working and no final answer
Wrong working141.12 on its own
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Question Acceptable Answer Mark Worth Worth 0
3 (a) Covalent Network/latticeIgnore order given
for bonding for structure
covalent onlynetwork/lattice onlycovalent plus incorrect descriptionof structurenetwork/lattice plus incorrectdescription of bonding
Polar covalent3DTetrahedralSingle bondsMolecular/discreetAny mention of ioniccancels correct answer
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Question Acceptable Answer Mark Worth Worth 0
(b) (i)
At least one of thesymbols must be shownin correct place.
Mixture of dots andcrosses acceptable.
Accept Lewis dotdiagram
Ignore inner electronsfor carbon.
Allow for one slip formisplaced electron.
Allow for one slip forsymbols.
Accept electron pair online of touching circles
1 or 0 Electrons missing.
One of the pair of sharedelectrons not in the overlap.
No symbols shown at all.
H
XX
C
H
HH
XX
XXXX C
H
XX
H
H
XX
XX XX Hor
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Question Acceptable Answer Mark Worth Worth 0
(ii) HC or
H H H
Use professional judgement to establishtetrahedral shape.
Symbols not required.
Accept outer electrondiagram if correct shapeis shown.
Dotted line and trianglenot necessary.
Professional judgement- Must not be square
planar.
HC
H HH
1 or 0 HH C H
H
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Question Acceptable Answer Mark Worth Worth 0
4 (a) (i) 25(%)Accept between 24 -26
If blank, check part (ii) and may award mark if 25% hasobviously been used in the calculation
1 or 0 75
(ii) 25/100 6 = 1515 on its own
Accept follow through from part (i) if it applies
1 or 0 - mark per arithmetic mistake
(b) 4 moles to 2 moles4 108g = 2 248
432 = 496108 = 108 496/432
= 124
OR
no of moles of Ag = 108/108= 001 moles
no of moles of Ag 2S = 001/2= 0005
GFM Ag 2S = 248Mass of Ag 2S = 0005 248
= 124
Ignore units/absence of units/ incorrect units givenCheck paper for indication of final answer.
1
1
- mark per arithmetic mistake,even if correct final answer is given
-1 mark if atomic numbers are used
-1 mark if incorrect chemical used incalculation
If they only have calculatedthe GFM for Ag 2S (as 248)
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Question Acceptable Answer Mark Worth Worth 0
5 (a) Heat the catalyst and then the liquid paraffin/mineral woolHeat catalyst first
1 or 0 Heat the catalyst (with no mentionof heating paraffin)Heat moved between the twochemicalsHeat moved along the test tubeHeat catalyst and the paraffin/wool
Heat paraffin then catalystHeat paraffin/woolDescription of type offlame used to burn
(b) To prevent suck-back or some description 1 or 0 BlowbackTube can smash/crackAir bubble could formPrevent an explosion orother vague answer
(c) (i) Aluminium oxide/A1 2O3/ formula must be correct(Aluminium) silicateOther silicate
1 or 0 Steel woolCorrect name and incorrectformula cancels
(ii) Allows reaction to occur at lower temperatureLower energy requiredLower activation energy
1 or 0 CheaperSaves energyCan be reusedRemains unchangedPrevents harmful gases
being producedDoes not affect outcome ofthe reactionDoes not need to be heatedTo change temperatureused
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Question Acceptable Answer Mark Worth Worth 0
(d) AdditionBrominationHalogenationsAdditionalBrominisation
1 or 0 Addition polymerisationAddition plus incorrectSaturation
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Question Acceptable Answer Mark Worth Worth 0
6 (a) H H O H H H
H C C C C C C H
H H H H HAllow one slip:one missing bond but not in carbonyl group orone missing hydrogen
Accept correct (partial) shortened structural formula
1 or 0 2 slips
(b) Heptan-4-one/heptan4one /heptane-4-one/hept-4-one/hept4one/hepta-4-one
Must have hept, 4, and one
1 or 0 Septan-4-oneAlkene ending given hepten-4-one-one missing
(c) 147 155approx 150 or any number within the rangeaccept a range within the tolerance
1 or 0 Any other value
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Question Acceptable Answer Mark Worth Worth 0
7 (a) (i) FermentationAnaerobic respiration
1 or 0 Brewing
(ii) Enzyme/biological catalystEnzyme proteinIgnore names of enzymes given
1 or 0 Any named enzymeProteinBacteria
(b) Yeast is denatured/destroyed/loses its shapeEnzyme is denatured/destroyed/loses its shapeYeast dies/is killed
1 or 0 Wont work at high temperaturesWorks best at lower temperaturesYeast works at optimumtemperaturesWorks best at body temperatureWorks best at room temperatureDoes not work as well at high
temperatures
Enzyme dies/killedYeast reacts with heat
(c) DistillationCorrect description of the distillation process to include
both boiling and condensation stagesFractional distillation
1 or 0 Boil itBoil it because alcohol andwater have different boiling
points
Separate off the alcoholRemove water byevaporationFractionatingFractionation
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Question Acceptable Answer Mark Worth Worth 0
8 (a) EstersAlkyl alkanoates
1 or 0 OrganicEster plus any incorrectanswer
(b) (i) HydrolysisHydrolysedAccept spelling variations of the above
1 or 0 HydrolysisationHydrolysationDe-esterification
(ii) H H H O
H C C C C
H H H OH
Allow 1 slip missing bond but not from COOH group or missing H but not from COOH group
Accept (partial) shortened structural formula
Ignore any attempt to draw alcohol
1 or 0 2 slips
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Question Acceptable Answer Mark Worth Worth 0
10 (a) Any value below 7Accept a range if it is below 7
1 or 0 0-7
(b) (i) As the temperature increases the solubility decreasesORAs the temperature decreases the solubility increases
Correct use of units in the description of the trend
Allow slip e.g. lemonade instead of CO 2
Correct cause and effectLooking for a trend
1 or 0 As the solubility of carbondioxide decreases, thetemperature increases.
It has 1.2 g l-1 at 30 oC and1.56 g l-1 at 20 oC
(ii) Correct extrapolation of lineValue must come from candidates graph +/- boxtolerancecross or point rather than line acceptable
1.90-1.94 if line not extrapolated
1 or 0 Approximations notacceptedIncorrect extrapolation ofline
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Question Acceptable Answer Mark Worth Worth 0
11 (a) Acid rainDissolved/absorbed SO 2Dissolved/absorbed NO 2/oxides of nitrogen/generic termDissolved/absorbed CO 2Dissolved/absorbed soluble non metal oxides
1 or 0 Free H + ions Nitrate pollutionPollutionSulphur dioxide
Nitrogen dioxideCarbon dioxide
(b) (i) Calcium, carbon, oxygenCa/C/O/O 2
all 3 for 1 mark
1 or 0 Any incorrect element willcancel
(ii) Water/H 2Ohydrogen/H 2
1 or 0 HAny incorrect formula
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Question Acceptable Answer Mark Worth Worth 0
12 (a) Stops air/oxygen or water/moisturePhysical barrier to air/oxygen or water/moistureStops iron losing electrons to oxygen and water
Ignore mention of salt if correct reference to water/oxygen
1 or 0 Painting provides barrierPhysical protectionPhysical barrierStops water, oxygen andhydrogen getting to itStops iron losing electronsLess water/oxygen
(b) (i) GalvanisingGalvanisation
1 or 0 Sacrificial protection
(ii) Zinc sacrifices itselfZinc gives sacrificial protectionZinc is being oxidised
Zinc corrodes (by losing electrons)
The zinc gives away its electrons (to the iron)Zinc is more reactiveZinc is higher up in the ECS(or reverse of above for iron)
If the word it is used it should refer to iron in the answer
1 or 0 Zinc displaces ironZinc is too strong for ironZinc rusts
Any mention of ions cancels
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Question Acceptable Answer Mark Worth Worth 0
13 (a) The reading on the pH probe shows 7/neutral(pH probe) turns green/becomes neutral/goes to7
pH turns to 7End point of neutralisation/complete neutralisation
1 or 0 Turns blue/any incorrectcolour
NeutralisationUntil reaction has finished
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Question Acceptable Answer Mark Worth Worth 0
(b) Moles of acid = C V= 01 002= 0002
1 mole to 2 molesmoles of NaOH = 0002 2 = 0004c = n/v
= 0004/005= 008
OR
H C V = OH C V2 01 20 = 1 C 50
4 = 50C
C = 4/50
= 008OR
CA VA = bCBVB a
0.1 x20 = 1CB x 50 2
CB = 0.1 x 20x 250
= 450
= 0.08
1
- per arithmetic error
- if cm 3 used instead of litres onlyin method 1
- if cm 3 and litres mixed inmethod 2/3
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Question Acceptable Answer Mark Worth Worth 0
14 (a) (i) LHS = copper/CuTop RHS = Iron/FeBottom RHS = 100cm 3 01mol l-1 all 3 for 1 mark
1 or 0
(ii) Repeated () to allow averages/mean () to becalculated
2 x More than one measurement takenCalculate average
Control of other variables
(b) (i) From right to left arrow should be on wires or veryclose to it
1 or 0 Arrow in solutionArrow in solution and onwires cancels
(ii) (good) conductor of electricityContains delocalised electronsConductsConductiveFree moving electrons
1 or 0 CheapInsolubleSolidUnreactive
[END OF MARKING INSTRUCTIONS]